When a starch is pre-cooked, it can then be used to thicken cold foods. It is then referred to as a pregelatinised or instant starch. Otherwise starch requires heat to thicken, or “gelatinise.” The actual temperature to gelatinise starch in excess of water depends on the type of starch. Pregelatinised starches are particularly widely used in convenience foods such as instant soups, instant sauces, instant gravies, instant beverages, salad dressing mixes and the like, in dairy foods such as instant puddings and the like, in bakery foods such as cake mixes, bakery creams and the like, and in instant baby and infant foods.
The terms “gelatinised” or “cooked” starch refers to swollen granules which have lost their polarisation crosses and which may or may not have lost their granular structure. The thermal processes generally employed to prepare pregelatinised starches include roll drying, extrusion, high temperature heating in alcohol/water systems and spray cooking/drying. The physical properties of the pregelatinised starches, in particular the wettability, the dispersibility and peak viscosity in cold water, are dependent on the process used to pregelatinise the starch.
Roll-dried and spray cooked/dried starches are the most widely used pregelatinised starches on the market. These starches generally have less thickening power and less gelling tendency than the corresponding granular starch upon gelatinisation. The loss in thickening and gelling potential is related to the partial destruction of the hydrated granular structure. Roll-dried starches typically have less thickening power compared to spray cooked/dried starches. From a thermodynamic perspective, both common processes, roll drying and spray cooking/drying, are also not very energy efficient. There is therefore a need for starches which have high thickening powers in cold liquids and can be produced via a process that is energetically more efficient compared with roll drying and spray cooking/drying. The process of this invention provides such starches.
Superheated steam as a drying medium is an emerging technology and relatively unknown. A study concerning this drying technology has been carried out by TNO Environment, Energy and Process Innovation, Appeldoorn, The Netherlands, report R 2004/239 “Industrial superheated steam drying”.
Frydman, A, in the thesis ‘Caractérisation expérimentale et modélisation d'un procédé séchage par pulverisation dans la vapeur d'eau surchauffée’, ENSIA, 1998, mentions that starch can be pregelatinised by superheated steam treatment.
JP61-280244 discloses the heat treatment of starch in the presence of superheated steam of temperatures between 105 and 350° C. for less than 5 minutes at gauge-pressures of less than 9 kg/cm2.
The process according to the present invention provides starch products with novel and superior functionalities than conventional pregelatinised starches.